Sanofi Just Spent $9.5 Billion on a Rare Disease You’ve Never Heard Of

🗝️ Key Points

• Sanofi (SNY, Financial) is making another bold move to cement its position in immunology, agreeing to acquire Blueprint Medicines (BPMC, Financial) for $129 a share in cash—plus up to $6 in milestone payments tied to future success of its next-gen drug candidate BLU-808.
• That pegs the total deal at around $9.5 billion, a 40% premium over Blueprint's 30-day average.
• Ayvakit, the only approved treatment for systemic mastocytosis (SM)—a rare and debilitating immune disorder—as well as a pipeline that could unlock broader inflammatory markets.Ayvakit is no science project.

Sanofi (SNY, Financial) is making another bold move to cement its position in immunology, agreeing to acquire Blueprint Medicines (BPMC, Financial) for $129 a share in cash—plus up to $6 in milestone payments tied to future success of its next-gen drug candidate BLU-808. That pegs the total deal at around $9.5 billion, a 40% premium over Blueprint’s 30-day average. The prize? Ayvakit, the only approved treatment for systemic mastocytosis (SM)—a rare and debilitating immune disorder—as well as a pipeline that could unlock broader inflammatory markets.

Ayvakit is no science project. The drug pulled in $479 million last year and nearly $150 million in Q1 2025, up more than 60% year-over-year. And this isn’t a one-hit wonder. Sanofi’s also picking up elenestinib (currently in Phase 2/3) and BLU-808—an oral KIT inhibitor that could have applications well beyond SM. The deal could plug directly into Sanofi’s immunology machine, which already includes Dupixent, and give it deeper reach among allergists and immunologists. CEO Paul Hudson called the deal a “strategic step forward” and suggested more acquisitions could be on the horizon.

If all goes to plan, the transaction closes by Q3 2025. It won’t move the needle on Sanofi’s 2025 financials, but it could begin lifting margins and earnings starting in 2026. Sanofi’s paying cash and tapping some fresh debt, but the tender offer isn’t contingent on financing. For Blueprint, it’s a scale-up opportunity—and a potential fast-pass to bring its early-stage science to more patients globally. The bet here is simple: Sanofi sees rare immunology not just as a niche, but as a high-margin, high-loyalty growth engine—and it’s not done building.

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